Case, if you had to spend ~$6 which would you purchase, goodnotes or zoomnotes?
I would try both the free trials and see what works for you. I really don't need a bunch of color or pen options. I need to have the same flexibility as a ball point pen and a sheet of paper. So GoodNotes works well for me.
See which trial works best for you. I don't think you would go wrong with either
Good luck.